Polymer electrolyte membrane fuel cells (PEMFC) are expected to provide higher efficiencies, fewer environmental pollutants, and reduced operating and maintenance costs than traditional power sources. An important component of a PEMFC is a polymer electrolyte membrane (PEM). The range of potential candidates for use as membrane materials in PEMFCs is limited by a number of requirements, including chemical, thermal, and mechanical stability, high ionic conductivity, and low reactant permeability. Developments have been made in the use of sulfonic acid functionalized polymers, including membranes such as Nafion® perfluorosulfonic acid membranes.
By lowering the equivalent weight of sulfonic acid functionalized polymers, the conductivity of such polymers can be improved, which is needed for improved fuel cell performance. Current proton-exchange membranes, such as Nafion® perfluorosulfonic acid membranes, are limited in how much their equivalent weight can be lowered before they lose their membrane forming properties, or before they exhibit excessive water swell. Low equivalent weight ionomers do not possess the crystallinity needed to impart integrity to their membranes and resist swelling or even solubility in water.
There is an ongoing need for conductive membranes suitable for use in applications such as fuel cells that exhibit good ionic conductivity while maintaining good crystallinity and hydration, as well as chemical, thermal, and mechanical stability at high temperatures.